fn main() {
    // first
    println!("Hello, world!");

    // 变量和可变性
    let mut x = 5;
    println!("x的值为：{}", x);
    x = 6;
    println!("x的值为：{}", x);

    // 变量和常量之间的差异
    const MAX_POINTS: u32 = 100_000;
    println!("最大值为：{}", MAX_POINTS);

    // 阴影
    let x = 5;
    let x = x + 1;
    let x = x * 2;
    println!("x的值为：{}", x);

    let spaces = "    ";
    println!("spaces的值为：{}", spaces);
    let spaces = spaces.len();
    println!("spaces的值为：{}", spaces);

    // 数据类型
    let guess:u32 = "22".parse().expect("Not a number!");
    println!("guess的值为：{}", guess);

    let x = (500, 6.4, "a");
    println!("x的值为：({},{},{})", x.0,x.1,x.2);
}